JP5985351B2 - Axial flow turbine - Google Patents

Description

  The present invention relates to an axial flow turbine used for a steam turbine, a gas turbine, or the like of a power plant.

In recent years, further improvement in turbine performance has been strongly demanded in order to improve the power generation efficiency of power plants. Although turbine performance is related to turbine loss, exhaust loss, mechanical loss, etc., it is considered to be most effective to reduce paragraph loss.
Paragraph losses include a variety of things.
(1) Airfoil loss due to the blade shape itself,
(2) Secondary flow loss due to flow not following the mainstream,
(3) There is a leakage loss caused by leakage of working fluid (steam, gas, etc.) to other than the main flow path.
The above leakage loss is
(A) Bypass loss caused when a part of the working fluid (leakage fluid) flows through a gap channel (bypass channel) other than the main channel and the energy of the leaking fluid is not effectively used,
(B) Mixing loss that occurs when leakage fluid flows from the gap channel into the main channel;
(C) Interference loss caused by leakage fluid flowing into the main flow path interfering with the downstream blade row, and the like.
In recent years, reducing not only the bypass loss but also the mixing loss and the interference loss has become an important issue. That is, not only reducing the flow rate (leakage amount) of the leaked fluid from the main channel to the gap channel, but also how to return the leaked fluid from the gap channel to the main channel without loss is an important issue.

  Therefore, in order to solve such a problem, it has been proposed to provide a plurality of guide plates on the downstream side of the gap flow path, and to change the flow direction of the leaking fluid to the main flow direction by these guide plates. (For example, refer to Patent Document 1).

JP 2011-106474 A

  However, the above prior art has room for improvement as follows. That is, in the prior art described in Patent Document 1, the leakage fluid is simply passed between the guide plates in order to turn the flow direction of the leakage fluid. For this reason, unless the number of guide plates is increased to narrow the gap between the guide plates, the effect of turning the direction of the flow of the leaking fluid cannot be sufficiently obtained, and the effect of reducing the mixing loss may not be sufficiently obtained. However, if the number of guide plates is increased and the interval between the guide plates is reduced, the contact area increases and the friction loss increases, which may cancel the effect of reducing the mixing loss.

  An object of the present invention is to provide an axial flow turbine capable of enhancing the effect of reducing mixing loss.

In order to achieve the above object, a representative present invention provides a plurality of stationary blades arranged on the inner circumferential side of a stationary body and arranged in the circumferential direction, and arranged on the outer circumferential side of the rotating body and arranged in the circumferential direction. A plurality of the moving blades, the plurality of stationary blades are disposed, the plurality of moving blades are disposed on the downstream side thereof, the main flow path through which the working fluid flows, and the outer periphery of the plurality of moving blades A shroud provided on the side, an annular groove formed in the stationary body and accommodating the shroud, formed between the groove and the shroud, and working fluid from the downstream side of the stationary blade of the main flow path A gap flow passage in which a part of the main flow passage flows in and flows out to the downstream side of the moving blade of the main flow passage, a plurality of seal fins provided in the clearance flow passage, and a downstream side of the gap flow passage a circulation flow generating chamber which is to form the circulation flow generating chamber, said shroud The wall facing and radially outer located radially inward of the rotating body from the peripheral surface, secured to said stationary body so as to be positioned on the circulation flow generating chamber, in the axial and radial direction of the rotary body And a plurality of extending shielding plates.

  In the present invention, a part of the working fluid (leakage fluid) flows into the clearance channel from the downstream side of the stationary blade of the main channel (in other words, the upstream side of the moving blade), and the leakage fluid flows into the clearance channel. It flows out to the downstream side of the rotor blade in the main flow path. At this time, the leaked fluid that has flowed into the gap flow channel from the downstream side of the stationary blade of the main flow channel is a flow having a large circumferential velocity component, but a part of it flows into the circulating flow generation chamber and collides with the shielding plate. By doing so, it is possible to generate a circulating flow in which the circumferential velocity component is suppressed. Further, the circumferential velocity component can be effectively reduced with respect to the flow of the leaked fluid flowing out from the gap flow channel to the downstream side of the rotor blade of the main flow channel by the interference of the circulation flow generated in this way. . Therefore, the flow direction of the leakage fluid can be matched with the flow direction of the working fluid (main flow fluid) that has passed through the rotor blade, and the effect of reducing the mixing loss can be enhanced.

  According to the present invention, the effect of reducing the mixing loss can be enhanced.

It is sectional drawing of the rotor axial direction which represents typically the partial structure of the steam turbine in the 1st Embodiment of this invention. FIG. 2 is a partial enlarged cross-sectional view of a portion II in FIG. 1 and shows a detailed structure of a gap channel in the first embodiment of the present invention. It is sectional drawing of the rotor circumferential direction in the cross section III-III in FIG. 1, and shows the flow in a main flow path. It is sectional drawing of the rotor circumferential direction in the cross section IV-IV in FIG. 1, and the flow in a clearance channel is shown with the flow in a mainstream furnace. It is a figure showing the distribution of the rotor blade outflow angle in the 1st Embodiment of this invention and a prior art, respectively. It is a figure showing the distribution of the rotor blade loss coefficient in the 1st Embodiment of this invention and a prior art, respectively. It is a partial expanded sectional view showing the detailed structure of the crevice channel in one modification of the present invention. It is a partial expanded sectional view showing the detailed structure of the crevice channel in other modifications of the present invention. It is a partial expanded sectional view showing the detailed structure of the clearance channel in the 2nd Embodiment of this invention.

  Hereinafter, an embodiment when the present invention is applied to a steam turbine will be described with reference to the drawings.

  FIG. 1 is a rotor axial cross-sectional view schematically showing a partial structure (paragraph structure) of a steam turbine in the first embodiment of the present invention. FIG. 2 is a partially enlarged cross-sectional view taken along a line II in FIG. 1 and shows a detailed structure of the gap channel. FIG. 3 is a cross-sectional view in the rotor circumferential direction taken along a cross-section III-III in FIG. 1 and shows a flow in the main flow path. FIG. 4 is a cross-sectional view of the rotor in the circumferential direction along section IV-IV in FIG. 1 and shows the flow in the gap flow path together with the flow in the main flow path.

  1 to 4, the steam turbine includes an annular diaphragm outer ring 1 (stationary body) provided on the inner peripheral side of a casing (not shown), and a plurality of steam turbines provided on the inner peripheral side of the diaphragm outer ring 1. Of the stationary blades 2 and an annular diaphragm inner ring 3 provided on the inner peripheral side of the stationary blades 2. The plurality of stationary blades 2 are arranged at predetermined intervals in the circumferential direction between the diaphragm outer ring 1 and the diaphragm inner ring 3.

  Further, the steam turbine includes a rotor 4 (rotating body) that rotates about the rotation axis O, a plurality of moving blades 5 provided on the outer peripheral side of the rotor 4, and an outer peripheral side of the moving blades 5 (in other words, And an annular shroud 6 provided on the blade tip side. The plurality of moving blades 5 are arranged at a predetermined interval in the circumferential direction between the rotor 4 and the shroud 6.

  The main flow path 7 for the steam (working fluid) is a flow path formed between the inner peripheral surface 8a of the diaphragm outer ring 1 and the outer peripheral surface 9 of the diaphragm inner ring 3, or the inner peripheral surface 10 of the shroud 6 (and the diaphragm outer ring 1). The inner peripheral surface 8b) of the rotor 4 and the outer peripheral surface 11 of the rotor 4 are constituted by a flow path or the like. A plurality of stationary blades 2 (in other words, one stationary blade row) are arranged in the main flow path 7, and a plurality of moving blades 5 (in other words, one moving blade) are arranged on the downstream side (right side in the drawing). The combination of the stationary blade 2 and the moving blade 5 constitutes one paragraph. Although only one stage is shown in FIG. 1 for convenience, in general, a plurality of stages are provided in the rotor axial direction in order to efficiently recover the internal energy of the steam.

  The steam (mainstream steam) in the main flow path 7 is flowing as indicated by white arrows in FIG. Then, the internal energy (in other words, pressure energy) of the steam is converted into kinetic energy (in other words, velocity energy) by the stationary blade 2, and the kinetic energy of the steam is converted into rotational energy of the rotor 4 by the moving blade 5. Is done. In addition, a generator (not shown) is connected to the end of the rotor 4, and the rotational energy of the rotor 4 is converted into electric energy by this generator.

  The flow of steam (main flow) in the main flow path 7 will be described in detail. Steam flows in from the leading edge side (left side in FIG. 3) of the stationary blade 2 at an absolute velocity vector C1 (specifically, an axial flow having almost no circumferential velocity component). Then, when passing between the blades of the stationary blade 2, the speed is increased and turned to become an absolute velocity vector C2 (specifically, a flow having a large circumferential velocity component), and the trailing edge side (right side in FIG. 3) ). Most of the steam flowing out of the stationary blade 2 collides with the moving blade 5 to rotate the rotor 4 at a speed U. At this time, the steam is decelerated and turned when passing through the moving blade 5, and changes from the relative speed vector W2 to the relative speed vector W3. Therefore, the steam flowing out from the moving blade 5 becomes an absolute velocity vector C3 (specifically, an axial flow having substantially the same circumferential velocity component as the absolute velocity vector C1).

  By the way, an annular groove portion 12 that houses the shroud 6 is formed on the inner peripheral surface of the diaphragm outer ring 1, and a gap channel (bypass channel) 13 is formed between the groove portion 12 and the shroud 6. . Then, a part of the steam (leakage steam) flows into the clearance channel 13 from the downstream side of the stationary blade 2 of the main channel 7 (in other words, the upstream side of the moving blade 5), and the leaked steam passes through the clearance channel 13. Then, it flows out downstream of the rotor blade 5 in the main flow path 7 (leakage flow). Therefore, the internal energy of the leaked steam is not effectively used, and a bypass loss occurs. In order to reduce this bypass loss, that is, in order to reduce the flow rate (leakage amount) of leaked steam from the main flow path 7 to the gap flow path 13, the gap flow path 13 is provided with a labyrinth seal.

  In the labyrinth seal of the present embodiment, annular seal fins 14A to 14D are provided on the inner peripheral surface of the groove 12, and these seal fins 14A to 14D are arranged at predetermined intervals in the rotor axial direction. The tip end portions (inner peripheral side edge portions) of the seal fins 14A to 14D have a wedge shape with a sharp cross section. On the outer peripheral side of the shroud 6, an annular step portion (protrusion portion) 15 is formed so as to be positioned between the first-stage seal fin 14 </ b> A and the fourth-stage seal fin 14 </ b> D.

Gap size D ₁ of the outer peripheral surface of the shroud 6 to tip and opposed to each seal fin, the flow rate of leaking steam while preventing contact of the stationary side and the rotary side is set as small as possible. The step size D ₂ of the step portion 15 is set, for example, two to three times the gap dimension D ₁ as described above. Therefore, the seal fins 14A, 14D, the seal fins 14B, from 14C, is longer by the amount of level difference _{D 2} mentioned above.

  The mainstream steam on the downstream side of the stationary blade 2 in the main flow path 7 is a flow (absolute speed vector C2) having a large circumferential speed component as described above, and the leaked steam flowing into the gap flow path 13 is also large. The flow has a circumferential velocity component. The leaked steam that has flowed into the gap flow path 13 is a gap (throttle) between the tip of the first-stage seal fin 14A and the outer peripheral surface of the shroud 6, and the tip of the second-stage seal fin 14B and the outer peripheral surface of the shroud 6. , The gap between the tip of the third-stage seal fin 14C and the outer peripheral surface of the shroud 6, and the gap between the tip of the fourth-stage seal fin 14D and the outer peripheral surface of the shroud 6 (throttle) ) In order. At this time, the total pressure of the leaked steam is reduced due to the throttle loss. Further, although the axial velocity of the leaking steam increases, the circumferential velocity does not vary substantially. That is, the leaked steam that has passed through the gap between the tip of the final-stage seal fin 14D and the outer surface of the shroud 6 is still a flow having a large circumferential velocity component.

  On the other hand, the mainstream steam that has passed through the moving blade 5 in the main flow path 7 is a flow (absolute velocity vector C3) that has almost no circumferential velocity component as described above. Therefore, suppose that the leaked steam that has passed through the gap between the tip of the final-stage seal fin 14D and the outer surface of the shroud 6 flows out to the downstream side of the rotor blade 5 in the main flow path 7 with the flow having a large circumferential velocity component. Then, the mixing loss increases.

  Therefore, as the greatest feature of the present embodiment, an annular protrusion 16 that protrudes toward the downstream end surface of the shroud 6 is provided on the downstream side surface of the groove portion 12 of the diaphragm outer ring 1. As a result, the circulation flow generation chamber 17 is formed on the downstream side of the gap flow path 13. The circulation flow generation chamber 17 includes a part of the inner peripheral surface of the groove portion 12 located downstream of the final-stage seal fin 14D, the downstream side surface of the groove portion 12, and the outer peripheral surface of the first projection portion 16 (the radially outer surface). ). A part of the leaked steam that has passed through the gap between the tip of the last-stage seal fin 14D and the outer peripheral surface of the shroud 6 flows into the circulation flow generation chamber 17 and collides with the downstream side surface and the like of the groove 12 to circulate. A stream A1 is generated.

  Furthermore, a plurality of shielding plates 18 arranged at predetermined intervals in the circumferential direction are fixed to the downstream side surface of the groove portion 12 (in other words, in the circulation flow generation chamber 17). The shielding plate 18 extends in the rotor axial direction and the rotor radial direction. In the present embodiment, the shielding plate 18 is a flat plate arranged so as to be perpendicular to the tangential direction of the rotation of the rotor 4. And the leaked steam (in other words, circulation flow A1) which flowed into circulation flow production | generation chamber 17 collides with the shielding board 18, and the circumferential direction velocity component of circulation flow A1 is suppressed (refer FIG. 4). . Due to the interference of the circulating flow A1 generated in this way, the circumferential velocity component is effectively removed from the leaked steam flow B1 flowing out from the clearance channel 13 to the downstream side of the rotor blade 5 of the main channel 7. (See FIG. 4). In other words, the circumferential velocity component can be effectively removed regardless of the circumferential velocity of the leaked steam as compared with the case where leaked steam is passed between the guide plates as described in Patent Document 1, for example.

  Note that the tip of the protrusion 16 is located on the inner side in the rotor radial direction from the outer peripheral surface of the shroud 6 facing the final-stage seal fin 14D. Accordingly, the leaked steam that has passed through the gap between the tip of the final-stage seal fin 14 </ b> D and the outer peripheral surface of the shroud 6 is likely to flow into the circulation flow generation chamber 17.

  Further, the protrusion 16 also plays a role of suppressing the radial velocity component with respect to the leaked steam flow B <b> 1 flowing out from the gap channel 13 to the downstream side of the rotor blade 5 of the main channel 7. In particular, the inner peripheral surface of the protrusion 16 extends from the outer side (upper side in FIG. 2) to the inner side (upper side in FIG. 2) from the upstream side (left side in FIG. 2) to the downstream side (right side in FIG. 2). 2), the leakage steam is directed in the rotor axial direction. The protrusion 16 also serves to prevent the steam from flowing back from the main flow path 7 to the gap flow path 13.

  Next, the effect of this embodiment will be described with reference to FIGS.

  FIG. 5 is a diagram showing the distribution of the rotor blade outflow angle in the present embodiment (solid line in the figure) and the distribution of the rotor blade outflow angle in the conventional technique (dotted line in the figure), and the vertical axis indicates the blade height in the main flow path 7. The horizontal axis indicates the outflow angle of the moving blade 5 (in other words, the absolute flow angle of steam on the downstream side of the moving blade 5). The outflow angle of the rotor blade 5 is based on the rotor axial direction (zero), and the absolute value of the outflow angle approaches 90 degrees as the circumferential speed increases with respect to the axial speed. FIG. 6 is a diagram showing the distribution of the blade loss coefficient in the present embodiment (solid line in the figure) and the distribution of the blade loss coefficient in the conventional technique (dotted line in the figure). The vertical axis indicates the blade height in the main flow path 7. The position in the vertical direction is shown, and the horizontal axis shows the loss coefficient of the moving blade 5.

  As described above, leaked steam flows into the gap channel 13 from the downstream side of the stationary blade 2 of the main channel 7 (in other words, upstream of the moving blade 5), and the leaked steam flows through the gap channel 13 to the mainstream. It flows to the downstream side of the moving blade of the path 7. At this time, the leaked steam flowing into the gap flow path 13 from the downstream side of the stationary blade 2 of the main flow path 7 is a flow having a large circumferential velocity component, and the tip of the final-stage seal fin 14D and the outer surface of the shroud 6 The leaked steam that has passed through the gap is also a flow having a large circumferential velocity component.

  And in the prior art which does not provide the projection part 16 and the shielding board 18 which were mentioned above, the leaking vapor | steam which flows out into the main flow path 7 from the clearance flow path 13 turns into a flow with a big circumferential speed component. On the other hand, the mainstream steam that has passed through the moving blade 5 in the main flow path 7 is a flow that has almost no circumferential velocity component as described above. Therefore, as shown in FIG. 5, although the flow angle is almost zero in the region other than the vicinity of the blade tip, the flow angle approaches -90 degrees in the region near the blade tip. Further, in the prior art, since the protruding portion 16 does not exist, the radial velocity of the leaked steam flowing out from the gap channel 13 to the main channel 7 is relatively high. Therefore, as shown in FIG. 5, the range in the blade height direction affected by the leaked steam is also relatively large. As a result, the mixing loss increases as shown in FIG.

  On the other hand, in the present embodiment, a circulating flow in which the circumferential velocity component is suppressed is generated on the downstream side of the gap flow path 13, and interference of the circulation flow causes the moving blades 5 of the main flow path 7 from the gap flow path 13. The circumferential velocity component can be effectively removed from the leaked steam flow that flows downstream. That is, the leaked steam flowing out from the gap channel 13 into the main channel 7 has a flow that has almost no circumferential velocity component. Therefore, as shown in FIG. 5, the flow angle is almost zero even in the region near the blade tip. Further, in the present embodiment, due to the presence of the protruding portion 16, the radial speed of the leaked steam flowing out from the gap channel 13 to the main channel 7 can be reduced. Therefore, as shown in FIG. 5, the range in the blade height direction affected by the leaked steam is also relatively small. As a result, as shown in FIG. 6, the mixing loss can be reduced and the stage efficiency can be improved.

  The effect of the present embodiment is greater when there are a plurality of paragraphs that are combinations of the moving blade rows and the stationary blade rows than when there is a single paragraph. In the prior art, as described above, the flow angle in the region near the blade tip is different from the flow angle in other regions, and the flow is twisted in the blade height direction. Since the inlet blade angle of the stationary blade does not change greatly in the blade height direction, if the flow described above flows into the downstream stationary blade, the interface boundary layer development and secondary flow growth are promoted, resulting in interference loss. Occurs. On the other hand, in this embodiment, as described above, the flow angle in the region near the blade tip is substantially the same as the flow angle in the other regions, and the flow is uniform in the blade height direction. Even if the flow described above flows into the stationary blade, the incidence of the stationary blade is not greatly shifted, and the occurrence of interference loss can be suppressed. That is, an increase in the secondary flow loss of the downstream stationary blade can be suppressed, and the downstream stage efficiency can be improved.

  In the first embodiment, as shown in FIG. 4, the circumferential interval (angle conversion) of the shielding plate 18 is substantially the same as the circumferential interval (angle conversion) of the moving blade 5 (in other words, paraphrase). For example, the case where the number of shielding plates 18 is the same as the number of moving blades 5) is taken as an example. However, the present invention is not limited to this, and modifications can be made without departing from the spirit and technical idea of the present invention. That is, even if the number of shielding plates 18 is less than the number of moving blades 5 depending on the circumferential speed of the leaked steam flowing into the gap flow channel 13 from the downstream side of the stationary blade 2 of the main flow channel 7, the first implementation described above. The same effect as the form can be exhibited. In such a case, the number of shielding plates 18 may be reduced from the number of moving blades 5.

  Further, in the first embodiment, the circumferential velocity of the mainstream steam on the downstream side of the moving blade 5 in the main flow path 7 (in other words, on the upstream side of the stationary blade 2) is substantially zero. In the above description, the case where the rotor 4 is arranged so as to be perpendicular to the tangential direction of rotation of the rotor 4 has been described as an example. However, the present invention is not limited to this, and modifications can be made without departing from the spirit and technical idea of the present invention. is there. That is, the shielding plate 18 may be slightly inclined in the rotor circumferential direction depending on the circumferential speed of the steam on the downstream side of the rotor blade 5 in the main flow path 7. Even in such a case, the same effect as the first embodiment can be obtained.

  In the first embodiment, as shown in FIG. 2, the case where no protrusion is provided on the downstream end surface of the shroud 6 has been described as an example. However, the present invention is not limited to this, and the downstream end surface of the shroud 6 is not limited thereto. Protrusions may be provided on the. Specifically, for example, as in a modification shown in FIG. 7, an inner protrusion 19 positioned on the inner side in the rotor radial direction (lower side in the drawing) from the protrusion 16 may be provided on the downstream end face of the shroud 6A. Good. The outer peripheral surface of the inner projecting portion 19 faces the inner peripheral surface of the projecting portion 16, and the outer side in the rotor radial direction from the upstream side (left side in the figure) to the downstream side (right side in the figure) in the rotor axial direction. It is inclined from the inside (upper side in the figure) to the inner side (lower side in the figure). In other words, a leakage steam guide channel is formed between the inner peripheral surface of the protrusion 16 and the outer peripheral surface of the inner protrusion 19. Thereby, as shown by arrow B2 in the figure, the flow direction of the leaked steam flowing out from the gap flow path 13 to the main flow path 7 can be more directed in the rotor axial direction. Therefore, the effect of reducing the mixing loss and the interference loss can be further enhanced, and the stage efficiency can be improved. In addition, the effect of preventing the backflow of steam can be enhanced.

  Or you may provide the outer side projection part 20 located in the rotor radial direction outer side (upper side in the figure) rather than the projection part 16 in the downstream end surface of the shroud 6B like the other modification shown, for example in FIG. The outer peripheral surface of the outer projection 20 extends from the inner side (lower side in the figure) to the outer side (upper side in the figure) from the upstream side (left side in the figure) to the downstream side (right side in the figure) in the rotor axial direction. It is inclined to. As a result, as indicated by an arrow B3 in the figure, the leaked steam that has passed through the gap between the tip of the last-stage seal fin 14D and the outer peripheral surface of the shroud 6B turns to the outer side in the rotor radial direction, and enters the circulation flow generation chamber 17. It becomes easy to flow in. Therefore, the circulation flow A1 can be increased, and the circumferential velocity component removal effect due to the interference of the circulation flow A1 can be enhanced. Therefore, the effect of reducing the mixing loss and the interference loss can be further enhanced, and the stage efficiency can be improved.

  Moreover, in the said 1st Embodiment and modification, although the labyrinth seal which has four steps | paragraphs of seal fins 14A-14D and the one level | step-difference part 15 was demonstrated as an example, it is not restricted to this, The meaning and technique of this invention Modifications can be made without departing from the concept. That is, the number of stages of the seal fins is not limited to four, and may be two, three, or five or more. Moreover, it does not need to have a level | step-difference part, and may have two or more level | step-difference parts. In these cases, the same effect as described above can be obtained.

  In the first embodiment, the final stage seal fin 14D is provided on the inner peripheral surface of the groove portion 12 of the diaphragm outer ring 1, and the tip of the protrusion 16 is a shroud facing the final stage seal fin 14D. The structure located on the inner side in the rotor radial direction from the outer peripheral surface of the rotor 6 has been described as an example. However, the present invention is not limited to this, and various modifications can be made without departing from the spirit and technical idea of the present invention. That is, the final-stage seal fin may be provided on the outer peripheral surface of the shroud 6. And the position of the front-end | tip of the projection part 16 is good also as a structure located in a rotor radial direction inner side from the front-end | tip (outer periphery) or root (inner periphery) of the seal fin of the last step, for example. In such a case, the same effect as described above can be obtained.

  A second embodiment of the present invention will be described with reference to FIG. Note that in this embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  FIG. 9 is a diagram illustrating a detailed structure of the gap channel in the present embodiment.

  In the present embodiment, a notch is formed at the downstream end of the shroud 6C. That is, the shroud 6C is positioned on the outer peripheral surface 21a opposed to the final-stage seal fin 14D, and on the outer side in the rotor radial direction (upper side in the drawing) with respect to the outer peripheral surface 21a. Has an outer peripheral surface 21b facing each other, and a stepped side surface 22 formed between the outer peripheral surface 21a and the outer peripheral surface 21b.

Gap size D ₁ of the outer peripheral surface of the tip and the shroud 6C opposed thereto of the seal fin, as in the first embodiment, the flow rate of leaking steam while preventing contact of the stationary side and the rotary side is as small as possible It is set to be. Further, the rotor radial dimension D ₃ (step dimension) of the step side surface 22 is set to, for example, 5 times or more (about 6 to 8 times in the present embodiment) of the gap dimension D ₁ described above. Therefore, the seal fins. 14D, the sealing fins 14C, is longer by the amount of level difference D ₃ described above. In other words, the tips of the seal fins 14D are located on the inner side in the rotor radial direction (lower side in the figure) from the outer peripheral surface 21b.

The rotor axial dimension _{H 3} between the seal fin 14C and the seal fins 14, the rotor axis between the rotor axial dimension _{H 1} or seal fins 14B and the seal fins 14C between the seal fins 14A and the seal fins 14B more than twice the dimension H ₂ (in this embodiment, 2 to 3 times) is set to. The rotor axial dimension H ₄ between the seal fins 14C and step side 22 is larger than the dimension H ₁ or H ₂ as described above.

  With the structure described above, the circulating flow defined by the last-stage seal fin 14D, the seal fin 14C one stage before the last, and a part of the inner peripheral surface of the groove 12 positioned between the seal fins 14C and 14D. A generation chamber 17A is formed. The leaked steam that has passed through the gap between the tip of the seal fin 14C and the outer peripheral surface 21b of the shroud 6C flows into the circulation flow generation chamber 17A and collides with the seal fin 14D and the like to generate the circulation flow A2. ing.

  Further, on the inner peripheral surface of the groove portion 12, the grooves 12 are arranged at predetermined intervals in the circumferential direction so as to be located between the seal fins 14 </ b> C and 14 </ b> D (in other words, located in the circulation flow generation chamber 17 </ b> A). A plurality of shielding plates 18A are fixed. The shielding plate 18 </ b> A extends in the rotor axial direction and the rotor radial direction, and in the present embodiment, the shielding plate 18 </ b> A is a flat plate arranged so as to be perpendicular to the tangential direction of the rotation of the rotor 4. And the leaked steam (in other words, circulation flow A2) which flowed into circulation flow production | generation chamber 17A collides with the shielding board 18A, and the circumferential direction speed component of circulation flow A2 is suppressed. Due to the interference of the circulating flow A2 generated in this way, the circumferential velocity component is effectively removed from the leaked steam flow B4 flowing out from the clearance channel 13 to the downstream side of the rotor blade 5 of the main channel 7. be able to. In other words, the circumferential velocity component can be effectively removed regardless of the circumferential velocity of the leaked steam as compared with the case where leaked steam is passed between the guide plates as described in Patent Document 1, for example.

  In the present embodiment, the inner peripheral surface 8b of the diaphragm outer ring 1A is located on the outer side in the rotor radial direction from the tips of the seal fins 14D. Thereby, the leaked steam flowing out from the clearance channel 13 to the downstream side of the rotor blade 5 of the main channel 7 is directed in the rotor axial direction. Further, even when the relative positional relationship between the stationary body side and the rotating body side is greatly shifted in the axial direction due to the difference in thermal expansion between the stationary body side and the rotating body side when the steam turbine is started, the downstream end of the shroud 6C and the diaphragm outer ring 1 are It is designed not to collide.

  Also in the present embodiment as described above, the effect of reducing the mixing loss and the like can be enhanced as in the first embodiment.

  In the above description, the steam turbine, which is one of the axial flow turbines, has been described as an application target of the present invention. However, the present invention is not limited to this, and may be applied to a gas turbine or the like. In this case, the same effect as described above can be obtained.

DESCRIPTION OF SYMBOLS 1,1A Diaphragm outer ring 2 Stator blade 3 Diaphragm inner ring 4 Rotor 5 Rotor blade 6, 6A, 6B, 6C Shroud 7 Main flow path 12 Groove part 13 Crevice flow path 14A-14D Seal fin 16 Protrusion part 17, 17A Circulation flow production | generation chamber 18, 18A Shielding plate 20 Outer protrusion 21a, 21b Outer peripheral surface 22 Step side surface

Claims (4)

A plurality of stationary blades arranged on the inner circumferential side of the stationary body and arranged in the circumferential direction;
A plurality of rotor blades provided on the outer peripheral side of the rotating body and arranged in the circumferential direction;
The plurality of stationary blades are disposed, the plurality of moving blades are disposed on the downstream side thereof, and a main flow path through which a working fluid flows,
A shroud provided on the outer peripheral side of the plurality of rotor blades;
An annular groove formed in the stationary body and containing the shroud;
A gap channel formed between the groove and the shroud, a part of the working fluid flows in from the downstream side of the stationary blade of the main channel, and flows out to the downstream side of the blade of the main channel; ,
A plurality of stages of sealing fins provided in the gap channel;
A circulation flow generation chamber formed on the downstream side of the gap channel;
A wall surface that forms the circulating flow generation chamber, is located on the radially inner side of the rotating body from the outer peripheral surface of the shroud and faces the radially outer side;
An axial flow turbine comprising: a plurality of shielding plates fixed to the stationary body so as to be positioned in the circulation flow generation chamber and extending in an axial direction and a radial direction of the rotating body. The axial turbine according to claim 1,
An annular first protrusion protruding from the downstream side surface of the groove toward the downstream end surface of the shroud,
The circulation flow generation chamber includes a part of an inner peripheral surface of the groove portion, a downstream side surface of the groove portion, and an outer periphery of the first protrusion portion, which are located downstream of the last-stage seal fin among the plurality of stages of seal fins. It is divided by plane ,
The axial flow turbine characterized in that the wall surface located radially inward of the rotating body and facing radially outward from the outer peripheral surface of the shroud is the outer peripheral surface of the first protrusion . The axial turbine according to claim 2, wherein
Provided on the downstream end surface of the shroud is an annular outer protrusion positioned radially outward of the rotating body from the first protrusion,
The outer circumferential surface of the outer protrusion is inclined from the inner side to the outer side in the radial direction of the rotating body from the upstream side to the downstream side in the axial direction of the rotating body. A plurality of stationary blades arranged on the inner circumferential side of the stationary body and arranged in the circumferential direction ;
A plurality of rotor blades provided on the outer peripheral side of the rotating body and arranged in the circumferential direction;
The plurality of stationary blades are disposed, the plurality of moving blades are disposed on the downstream side thereof, and a main flow path through which a working fluid flows,
A shroud provided on the outer peripheral side of the plurality of rotor blades;
An annular groove formed in the stationary body and containing the shroud;
A gap channel formed between the groove and the shroud, a part of the working fluid flows in from the downstream side of the stationary blade of the main channel, and flows out to the downstream side of the blade of the main channel; ,
A plurality of stages of sealing fins provided in the gap channel;
A circulation flow generation chamber formed on the downstream side of the gap channel;
A plurality of shielding plates fixed to the stationary body so as to be located in the circulation flow generation chamber and extending in the axial direction and the radial direction of the rotating body,
The plurality of stages of seal fins are provided on the inner peripheral surface of the groove,
The shroud is positioned on the outer side in the rotor radial direction from the first outer peripheral surface of the plurality of stages of seal fins, the first outer peripheral surface facing the last stage of the fins, and one before the last. A second outer peripheral surface opposed to the seal fin of the step, and a step side surface formed between the first outer peripheral surface and the second outer peripheral surface;
The tip of the final stage seal fin is located on the inner side in the rotor radial direction from the second outer peripheral surface,
The rotor axial dimension between the last-stage seal fin and the last-stage seal fin, and the rotor axial dimension between the final-stage seal fin and the step side surface, Larger than the axial dimension of the rotor between the seal fins,
The circulation flow generation chamber is defined by the last-stage seal fin, the one-stage previous-stage seal fin, and a part of the inner peripheral surface of the groove portion located between the seal fins. An axial flow turbine.

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